The present invention relates to systems and methods for monitoring wear of, and/or displacement between, artificial joint members, vertebrae, segments of fractured bones, and dental implants. More specifically, embodiments of the present invention relate to detection systems capable of determining a distance between, for example, joint members of an artificial joint or between vertebrae, thus enabling to determine, for example, relative displacement therebetween.
Artificial Joints
Total joint arthroplasty is an operation involving the replacement of a damaged joint with an artificial joint assembly in order to restore motion to the joint and function to the muscles and ligaments and other soft tissue structures that operate and control the joint.
The operation is typically performed on individuals with a painful, disabling arthritic joint that is no longer responsive to conservative treatment regimens. This operation typically entails implantation of two or more artificial joint members into respective natural joint members so as to replace deteriorated natural articulating surfaces with artificial equivalents.
Artificial joint assemblies have been devised for a variety of joints including hips, knees, ankles, shoulders, elbows, fingers, toes and wrists. Typically, components of artificial joints such as that shown in, for example, U.S. Pat. No. 4,068,324 to Townley et al. mimic the structure and function of joint members of a natural joint, thus providing as natural as possible articulation motion.
While artificial joint components are designed to provide stable and permanent attachment to the natural adjacent body tissue(s), at attachment interfaces, motion and/or loosening of the artificial joint member can occur, resulting in artificial joint relocation, which can lead to a loss of function, bone deterioration and tissue debris generation.
Such relocation can lead to an increase in wear to the articulating surfaces of the artificial joint. Such wear typically results in reduced function of the artificial joint and, in addition, produces joint debris which are expelled from the joint area to the surrounding tissues and may cause adverse reactions, such as inflammatory granulatoma, in these tissues.
The debris expelled from the artificial joint includes microscopic particles typically measuring up to a few microns in size. These particles provoke various tissue reaction, which affect the bones hosting the artificial joint implant.
The type and severity of the biological reaction to wear generated particles depend mainly on the physical properties and to a lesser degree also on the chemical properties of the wear particles. For example, in joints which include polyethylene component three types of particles are observed, chunks, flakes and granules. The granules, which are approximately one micron in size, are responsible for an intense inflammatory reaction. The histology is characterized by phagocytosis of the particles, resulting in large conglomerations of macrophages due to their inability to digest the polyethylene. The inflammatory process is accompanied by release of biochemical mediators such as prostaglandins and interleukins that cause absorption of the host native bone. Wear particles of other plastics, such as acetyl-copolymer, are of similar physical shapes but may cause an even more intense reaction.
Wear in metallic and ceramic joints is typically characterized by small granules which are taken in by macrophages, leading to a similar biochemical reaction to that caused by plastics.
As a wear of a joint progresses and larger amount of particles are expelled to the surrounding tissues, further bone absorption and loosening of the joint implant may occur. Such loosening of a prosthetic joint implant and damage to surrounding tissues is often left undetected in a patient even if regularly checked by a physician. Most modern methods currently employed for determining the extent of loosening and/or wear of an artificial joint, rely upon either X-ray, computer tomography, isotope bone scan or magnetic resonance to image the implanted joint and are of insufficient accuracy or technically difficult to perform and/or interpret even by highly skilled professionals. In fact, the most modern joint replacement assemblies incorporate metal backed plastic components, metallic components, or ceramic components within metallic shells and as such the available imaging methods cannot produce sufficient contrast in order to determine artificial joint loosening and/or articulating surface wear.
As a result of inefficient detection methods, oftentimes the only indication of early joint loosening is the pain and discomfort suffered by the patient. Oftentimes bone absorption progresses to a stage necessitating replacement surgery using larger implants, and/or bone grafts to accommodate for the lost bone tissue. The prognosis for success and service life of the implant after such a corrective operation is less predictable and depends, among other factors, on the extent of bone absorption suffered. If performed relatively early on, such corrective surgery has an increased chance of success. Therefore, a method capable of detecting the extent and depth of wear of the articulating surfaces of an artificial joint or capable of detecting minute displacement of artificial joint components which are fixed within the bone is of paramount importance both to the patient and the treating physician.
The Spine
The spine is a column of individual vertebrae. Within the spinal column, vertebrae inter-articulate via three joints which form a tripod-like configuration ground the disc occupying the space between the bodies (anteriorly) and the two facet joints (posteriorly).
Degenerative processes of the spine affect all three joints and causes reduction of the disc space in between the vertebrae. Spinal injury may cause instability and loss of bone and may require surgical fusion of the affected vertebrae or vertebral replacement. Fusion is effected by a variety of techniques such as applying bone graft in the damaged disc spaces or by utilizing implanted fixation devices such as screws, cages, plates, rods or hooks.
If fusion is unsuccessful, partial or total lack of union between the vertebrae (non-union) leads to a painful condition which arises from the motion existing between the vertebrae. Such motion, which is oftentimes difficult to detect, often requires additional surgical intervention.
Therefore accurate measurements of implant displacement and of pathological motion during the post operative follow up period as well as subsidence of motion (fusion) is of paramount importance.
Dental Implants
Dental implants are typically composed of a metallic (or other biocompatible material) fixture which is anchored within the maxillary or mandibular bone, a post (e.g., rod or screw) which is attached to the fixture and a prosthetic tooth (typically referred to as a crown, or a cap) which is fitted over the post.
The stability of the implant is essential for longevity thereof and for the preservation of the bone stock. A loose dental implant will cause absorption of bone and further deterioration of the bone stock, often requiring bone reconstruction using various grafting procedures. Thus, it is in the interest of both patient and dental surgeon to detect denial implant loosening prior to bone deterioration.
Bone Fractures
Following traumatic or intentional (osteotomy) bone fractures, natural bone processes unite the fractured or broken bone segments. Oftentimes, the exact time of union remains uncertain and as such, the duration of treatment is oftentimes unnecessarily prolonged.
In addition, when bone segments fail to properly unite, the resulting state of non-union can lead to pain and loss of function in the fractured or broken member.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system and method which enable to monitor relative wear and/or displacement in artificial joints, vertebrae, segments of fractured bones or dental implants thus enabling accurate monitoring of, for example, the state of an implant following an implantation procedure or the state of a bone following a traumatic or intentional fracture.
According to one aspect of the present invention there is thus provided a distance measurement system, comprising at least one resonant circuit, at least one magnetic element with predetermined magnetic properties, a transmitter operable to transmit an electromagnetic pulse, a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and an analyzer operable to analyze an amplitude envelope property of the oscillations, to thereby determine a distance between the resonant circuit and the magnetic element. In an embodiment, the magnetic element is ferromagnetic. In another embodiment the magnetic element is paramagnetic. In an additional embodiment, the analyzer is operable to determine the amplitude envelope property from an absolute value of amplitudes of the oscillations. In another embodiment the analyzer is operable to determine the amplitude envelope property from relative amplitude values of more than one cycle of the oscillations. In an embodiment the amplitude envelope property is an amplitude rate of decay. In an additional embodiment the analyzer is operable to determine the distance between the resonant circuit and the magnetic element additionally from frequency properties of the oscillations.
In a preferred embodiment the distance measurement system comprises more than one resonant circuit, to thereby determine more than one distance between the resonant circuits and the at least one magnetic element. Another embodiment is operable to determine the distance between the resonant circuits and the at least one magnetic element in more than one dimension. In another embodiment the more than one resonant circuits are operable to resonate at different frequencies.
Another embodiment comprises more than one magnetic element, to thereby determine more than one distance between the at least one resonant circuit and the magnetic elements. Another embodiment preferably, is operable to determine the distance between the at least one resonant circuit and the magnetic elements in more than one dimension.
Another embodiment comprises more than one resonant circuit and more than one magnetic element, to thereby determine more than one distance between the resonant circuits and the magnetic elements. Another embodiment preferably is operable to determine the distance between the resonant circuits and the at least one magnetic element in more than one dimension.
In a preferred embodiment the analyzer comprises a look-up table, comprising relationships between measured oscillations end distances. In another embodiment the relationships are per-system relationships. In an additional embodiment, the relationships comprise in-situ calibrations.
According to another aspect of the present invention there is thus provided a method for assembling a distance measurement system, comprising the steps of: placing a resonant circuit at a first location, placing a magnetic element with predetermined magnetic properties at a second location, providing a transmitter for transmitting an electromagnetic pulse to the resonant circuit, providing a detector for detecting oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and providing oscillations, to thereby determine a distance between the first location and the second location. In an embodiment, the analyzer comprises a look-up table of relationships between measured oscillations and distances, and wherein the look-up table values are established for each one of a predetermined set of distances by performing for each predetermined distance the steps of transmitting an electromagnetic pulse to the resonant circuit, detecting oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and measuring an amplitude envelope property of the detected oscillations, to thereby establish a look-up table value for the distance.
According to yet another aspect of the present invention there is thus provided a method for measuring the distance between a first location comprising a resonant circuit and a second location comprising a magnetic element, comprising the steps of transmitting an electromagnetic pulse to the resonant circuit, detecting oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and analyzing an amplitude envelope property of the detected oscillations, to thereby determine a distance between the first location and the second location. In a preferred embodiment, the step of analyzing an amplitude envelope property further comprises comparing information detected from the emitted oscillations to information in a look-up table, of relationships between measured oscillations and distances. Another embodiment comprises obtaining the amplitude envelope property from an absolute value of amplitudes of the oscillations. Another preferred embodiment comprises obtaining the amplitude envelope property from relative amplitude values of more than one cycle of the oscillations. Another embodiment, comprises making use of an amplitude rate of decay as the amplitude envelope property. Another embodiment comprises additionally detecting the distance from frequency properties of the detected oscillations.
According to still another aspect of the present invention there is thus provided a distance measurement system utilizing eddy currents for energy dissipation, the system comprising: at least one resonant circuit, at least one magnetic element with predetermined magnetic properties, a transmitter operable to transmit an electromagnetic pulse, a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse, and an analyzer operable to analyze an amplitude envelope property of the oscillations as an indicator of eddy current induced energy dissipation, to thereby determine a distance between the resonant circuit and the magnetic element.
According to yet an additional aspect of the present invention there is thus provided an artificial joint system comprising: (a) at least one artificial joint member having an articulating surface and a bone attachment portion, the bone attachment portion being for attaching the at least one artificial joint member to at least one natural bone of a joint when implanted within an individual; (b) a detection system implanted within, or attached to, the at least one artificial joint member and the at least one natural bone of the joint the at least one detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; and (c) an extracorporeal unit including; (i) a transmitter operable to transmit an electromagnetic pulse; (ii) a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse; and (iii) an analyzer operable to analyze all amplitude envelope property of the oscillations, the amplitude envelope property being indicative of a distance between the resonant circuit and the magnetic element and thus of a distance between the at least one artificial joint member and the at least one natural bone of the joint.
According to still another aspect of the present invention there is thus provided, a method of determining a parameter associated with relative displacement between an artificial joint member and a natural bone of a joint to which it is attached, the method comprising: (a) providing a detection system implanted within, or attached to, at least one artificial joint member and at least one natural bone of a joint, the detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; (b) extracorporeally energizing the detection system so as to receive outside the body an information signal including oscillations emitted by the resonant circuit in response to the energizing; and (c) processing the information signal being received so as to yield an amplitude envelope property of the oscillations, the amplitude envelope being indicative of a distance between the resonant circuit and the magnetic element, and thus of a distance between the at least one artificial joint member and the at least one natural bone of the joint.
According to yet an additional aspect of the present invention there is thus provided an artificial joint system comprising: (a) an artificial joint assembly implantable within an individual, the artificial joint assembly including a first artificial joint assembly member having a first articulating surface and further including a second artificial joint assembly member having a second articulating surface, the first and the second articulating surfaces being in articulating engagement therebetween; (b) a detection system implanted within or attached to, the artificial joint assembly, the detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; and (c) an extracorporeal unit including: (i) a transmitter operable to transmit an electromagnetic pulse, (ii) a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse; and (iii) an analyzer operable to analyze an amplitude envelope property of the oscillations, the amplitude envelope property being indicative of a distance between the resonant circuit and the magnetic element and thus of a distance between the first artificial joint assembly member and the second artificial joint assembly member.
According to still an additional aspect of the present invention there is thus provided a method, of determining a parameter associated with wear or relative displacement of an artificial joint, the method comprising the steps of, (a) providing an artificial joint assembly system including: (i) an artificial joint assembly implantable within an individual, the artificial joint assembly including a first artificial joint assembly member having a first articulating surface and further including a second artificial joint assembly member having a second articulating surface, the first and the second articulating surfaces being in articulating engagement therebetween; and (ii) a detection system implanted within, or attached to, the artificial joint assembly, the detection system including at least one resonant circuit element; and at least one magnetic element having predetermined magnetic properties; (b) extracorporeally energizing the detection system so as to receive outside the body an information signal including oscillations emitted by the resonant circuit in response to the energizing; and (c) processing the information signal being received so as to yield an amplitude envelope property of the oscillations, the amplitude envelope being indicative of a distance between the resonant circuit and the magnetic element, and thus of a distance between the first artificial joint assembly member and the second artificial joint assembly member.
In a preferred embodiment the at least one artificial joint member includes al least two artificial joint members, each attached to a specific natural bone of the joint of the at least one natural bone of the joint, whereas the articulating surfaces of the at least two artificial joint members are configured to allow articulating engagement therebetween.
In a preferred embodiment the at least one resonance circuit element includes a plurality of distinct resonance circuit elements each producing a distinct signal of oscillating frequency upon reception of the electromagnetic pulse, the distinct signal being a function of a distance between a specific resonance circuit element of the plurality of distinct resonance circuit elements and the at least one magnetic element.
In a preferred embodiment the at least one artificial joint member forms a part of an artificial joint selected from the group consisting of an artificial shoulder joint, an artificial hip joint, an artificial knee joint, an artificial elbow joint, an artificial ankle joint, an artificial wrist joint, an artificial carpo-metacarpal joint, an artificial metacarpo-phalangeal joint, an artificial interphalangeal joint and an artificial metatarso-phalangeal joint.
In a preferred embodiment the at least one artificial joint member is fabricated from at least one material selected from the group consisting of stainless steel, titanium alloy, cobalt alloy, polyethylene or other polymers, ceramics and composites materials.
In a preferred embodiment the at least one resonance circuit element is implanted within, or attached to, the bone attachment portion of the at least one artificial joint member, and further wherein the at least one magnetic element is implanted within, attached to, or forms a part of the bone attachment portion of the at least one artificial joint member.
In a preferred embodiment the first and the second artificial joint assembly members each include a portion distant to the articulating surface thereof, the portion being for attaching each of the first and the second artificial joint assembly members to a natural bone of a joint when implanted within the individual,
According to a further aspect of the present invention there is thus provided a system for monitoring displacement between vertebrae comprising: (a) a detection system implanted within, or attached to, the vertebrae, the detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; (b) an extracorporeal unit including: (i) a transmitter operable to transmit an electromagnetic pulse; and (ii) a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse; and (iii) an analyzer operable to analyze an amplitude envelope property of the oscillations, the amplitude envelope property being indicative of a distance between the resonant circuit and the magnetic element and thus of a distance between the vertebrae.
According to still a further aspect of the present invention there is thus provided a method of determining a parameter associated with relative displacement of vertebrae, the method comprising the steps of: (a) attaching or implanting a detection system within or upon the vertebrae, the detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; (b) extracorporeally energizing the detection system so as to receive outside the body an information signal including oscillations emitted by the resonant circuit in response to the energizing; and (c) processing the information signal being received so as to yield an amplitude envelope property of the oscillations, the amplitude envelope being indicative of a distance between the resonant circuit and the magnetic element, and thus of a distance between the vertebrae,
In a preferred embodiment at least one of the vertebrae is an artificial vertebra. According to yet a further aspect of the present invention there is provided
According to yet a further aspect of the present invention there is thus provided a system for monitoring displacement between a dental implant and a bone in which it is anchored comprising: (a) a detection system implanted within, or attached to, the dental implant and the bone, the detection system, including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; and (b) an extracorporeal unit including: (i) a transmitter operable to transmit an electromagnetic pulse: (ii) a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse; and (iii) an analyzer operable to analyze an amplitude envelope property of the oscillations, the amplitude envelope property being indicative of a distance between the resonant circuit and the magnetic element and thus of a distance between the dental implant and the bone.
According to still a further aspect of the present invention there is thus provided a method of determining a parameter associated with relative displacement between a dental implant and a bone in which it is anchored, the method comprising the steps of: (a) providing a detection system within the dental implant and the bone, the detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; (b) extracorporeally energizing the detection system so as to receive outside the body an information signal including oscillations emitted by the resonant circuit in response to the energizing, and (c) processing the information signal being received so as to yield an amplitude envelope property of the oscillations, the amplitude envelope being indicative of a distance between the resonant circuit and the magnetic element and thus of a distance between, the dental implant and the bone.
According to still a further aspect of the present invention there is thus provided a system for monitoring displacement between bone segments of a fractured or a broken bone comprising: (a) a detection system implanted within, or attached to, the bone segments, the detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; and (b) an extracorporeal unit including: (i) a transmitter operable to transmit an electromagnetic pulse; (ii) a receiver operable to detect oscillations emitted by the resonant circuit in response to the electromagnetic pulse and (iii) an analyzer operable to analyze an amplitude envelope property of the oscillations, the amplitude envelope property being indicative of a distance between the resonant circuit and the magnetic element and thus of a distance between the bone segments of the fractured or broken bone.
In a preferred embodiment the system further comprising at least one anchor element being for attaching the detection system to the bone segments.
In a preferred embodiment the at least one anchor element forms a part of an implant.
In a preferred embodiment the implant serves for inter-fixating the bone segments.
According to still a further aspect of the present invention there is thus provided a method of determining a parameter associated with relative displacement between bone segments of a fractured or broken bone, the method comprising the steps of (a) attaching or implanting a detection system within or upon the bone segments, the detection system including: (i) at least one resonant circuit element; and (ii) at least one magnetic element having predetermined magnetic properties; (b) extracorporeally energizing the detection system so as to receive outside the body an information signal including oscillations emitted by the resonant circuit in response to the energizing; and (c) processing the information signal being received so as to yield an amplitude envelope property of the oscillations, the amplitude envelope being indicative of a distance between the resonant circuit and the magnetic element, and thus of a distance between the bone segments of the fractured or broken bone.
The present invention successfully addresses the shortcomings of the presently known configurations by providing systems and methods with which a wear and/or displacement of members of an implanted artificial joint assembly, or displacement of bone segments, vertebrae or dental implants can be determined in an easy and accurate manner.